The invention relates to a parallel and outer axial rotating piston compressor with at least one helical main rotor and correspondingly at least one auxiliary rotor meshing therewith.
Such a rotating piston compressor is known, e.g., from DE-OS No. 2 505 113, the disclosure of which is incorporated herein by reference. The Offenlegungsschrift deals in particular with the shape of the tooth surfaces of the auxiliary rotor, in order to keep the blow-hole of the compressor toothing as small as possible. This is achieved in that the contact line along which the tooth flanks of a tooth each of main and auxiliary rotors, respectively, of a tooth pair in engagement adjoin, does not reach to the housing edge which is produced by the section of the two housing bores (see also Rinder, Springer Verlag, Vienna, N.Y., 1979, p. 72 ff, which is also incorporated herein by reference).
Similarly, U.S. Pat. No. 2,622,787 deals with the reduction of leakage produced due to the blow-hole. The disclosure of this patent is also incorporated herein by reference.
These and other known rotating piston compressors have symmetrical and non-symmetrical tooth profiles composed of differently dimensioned curve segments which are mathematically often not uniformly definable. In general, the teeth are deeply cut in, see also Rinder, Screw Compressors, p. 28, FIG. 11, where the construction and build-up of a non-symmetrical rotor is described in more detail.
The rotors of screw compressors must be produced with the greatest precision possible to keep leakage as small as possible; thus, expensive and costly tools and tool machines are necessary. Due to the complicated shape of the individual profiles, special cutters are required and the production of a rotor demands several work steps (e.g., pre-cutting with so-called roughing cutters, and then finishing with finishing or fine cutters). A cutter set for a rotor pair can be expensive, the cost depending on the diameter. The cost for final inspection is added to this.
Rotating piston compressors are available on the market which have different output volumes to satisfy each desired requirement. Accordingly, the manufacturers offer compressor series wherein the distance between the steps is chosen relatively large because of the expensive production, so that not too many expensive tools must be produced and kept in storage. Consequently, the individual rotating piston compressor types of a series are not operated in their optimal region or near the optimal region but over a larger region. In FIG. 1, the specific rate of power input (kW/m.sup.3 /min) is plotted versus the output volume (m.sup.3 /min). On the abscissa, the circumferential speed of a rotor or its rotational speed could be plotted; this would change nothing of the qualitative statement. The optimal operational point lies at point A on the drawn curve, as can be seen in FIG. 1. The rotating piston compressors on the market run in the region BAC that is not exclusively in or near the optimal region, which would lie approximately at B'AC', in order to let the output volume stream of a type link-up with the next larger type without a gap. The expansion of the output amount region of each type must be achieved by variation of the rotational speed with transmission gears (belt or toothed-wheel gearing, or by regulation of the rotational speed of the drive motor). If one wanted to operate the rotating piston compressor in the region B'AC', the output volume stage would have to be decreased. But to achieve this as mentioned above, a larger number of rotating piston compressor types would be required and a larger number of expensive tools.
It is the object of the invention to create a rotating piston compressor of the initially described type which is easy to produce and which requires only relatively inexpensive tools for manufacturing the profiles. Furthermore, the dimensional control should be carried out precisely, economically and simply.